It is proposed to use synthetic antigens to investigate a number of parameters of the immune response. As an extension of findings that spacers between the haptenic and immunogenic determinants of bifunctional antigens modulate the anti-hapten response, the upper limit of spacer size will be determined by synthesizing bifunctional molecules with large rigid spacers. Monofunctional molecules which differ only slightly in structure but profoundly in immunogenicity will be compared with respect to macrophage processing, tolerogenicity and induced changes in levels of prostaglandins and cyclic nucleotides in lymphoid cells. The object is to elucidate at what stage of antigen-immune system interaction discrimination between immunogens and non-immunogens takes place. Monofunctional immunogens which differ in the specificity of their induced delayed hypersensitivity responses will be compared with respect to the specificity of tolerance and helper activity they induce, in order to assess the cellular relationships of these functional activities. It will be determined if the unresponsiveness induced by monofunctional antigens is mediated by suppressor T cells. Finally, it will be determined if T cells in A/J mice specific for the azobenzenearsonate epitope bear surface molecules which share the cross-reactive idiotype found on antibodies, and, if so, whether the molecules are biosynthetic products of T cells.